1. Field of the Invention
The present invention relates to a thin-film magnetic head, a head gimbal assembly, and a hard disk drive.
2. Related Background of the Invention
As magnetic recording media such as hard disks increase their density, thin-film magnetic heads are required to improve their performances. Thin-film magnetic heads encompass reproducing heads including a magnetoresistive device (hereinafter referred to as MR device) for reading. As a characteristic of a reproducing head, it is required that Barkhausen noise be low. For reducing Barkhausen noise, hard magnetic layers are disposed so as to hold the MR device therebetween, and a bias magnetic field is applied to the MR device, such that a free layer included in the MR device is turned into a single domain.
Meanwhile, for responding to a further higher magnetic recording density, reproducing heads are required to further narrow their gaps and tracks. However, narrowing the gaps and tracks makes it harder to apply the bias magnetic field effectively to the MR device. In particular, as the track width becomes narrower, Barkhausen noise is more likely to occur. For suppressing the occurrence of Barkhausen noise, it has been known to provide a bias magnetic field applying film for applying a bias magnetic field to an MR device as a laminate film composed of a hard magnetic layer (made of a hard magnetic material containing Co, such as CoPt alloy or CoCrPt alloy) and a highly magnetically saturated magnetic layer (made of FeCo alloy), so as to enhance the saturation magnetization of the bias magnetic field applying film as a whole (see, for example, Patent Document 1: Japanese Patent Application Laid-Open No. HEI 10-312512, and Patent Document 2: Japanese Patent Application Laid-Open No. HEI 10-312514).